Title: The extent and effect of genetic drift and natural selection on the
speciation of Cepaea populations
Introduction
Evolution is driven by natural selection and genetic drift. Selection acts
with direction based on driving heritable phenotypic adaptations to the
environment.<span style="color: #ff0000; font-family: arial,helvetica,sans-serif; white-space: normal;"> what about balancing selection</span> Conversely drift acts on the genetic frequencies with chance
and no regard for phenotype. The question at hand is to what extent does
each factor contribute to the final outcome of phenotypic frequencies?
A phenotypic trait that provides evidence for both selection and drift in
a population is that of Polymorphism<span style="color: #ff0000; font-family: arial,helvetica,sans-serif; white-space: normal;"> polymorphism is not a phenotypic trait, as I understand the term</span>. This is the biological instance when
there is more than one morphological appearance<span style="color: #ff0000; font-family: arial,helvetica,sans-serif; white-space: normal;"> in modern terms, surely its the existence of multiple alleles- you might have genetic polymorphism not discernable in the phenotype</span> of a species within the
same panmictic (random mating) population, habitat and time frame (Ford
1965).
Cepaea nemoralis (the grove snail) is a renowned example of polymorphism.
Their shells show extensive amounts of diversity ranging in colour (brown,
pink and yellow) and also in the number of longitudinal bands present
(five to none). Such distinct phenotypes, along with widespread
populations, unsuspecting nature and their ability to cross-fertilise as
hermaphrodites make these molluscs’ ideal candidates for investigation.
say something about the mapping of genotype onto phenotype
Through the following experiment we aim to determine the extent and effect
of genetic drift and natural selection on the speciation of snail
populations in a particular habitat. We will do this by observing
historical frequencies of snail phenotypes (in the form of discarded
shells and fragments) in given areas, and comparing them with the
phenotypes of the current living population in the same areas. The results
will determine which phenotypes are being more frequently selected for. what is the logic here, if the dead are different from the live, that implies the allele frequency has changed, but that could be due to drift could it not?
Further to this we will compare the results between 3 or 4 populations to
discern whether the resulting phenotypes are based on natural selection or
genetic drift. how will you tell them apart?
Here we hypothesize that we will observe a relatively constant correlation
between the phenotypic frequency of dead and living snails in a particular
location.
We can predict that the observations will show that natural selection is
working towards fixing a particular phenotype if those in historical
frequencies are the same as in current frequencies. what if the environment has changed. Eg you could see that bushes had recently been cut down to make more open areas However we can also
predict that the occurrence of genetic drift within a population will give
rise to varying phenotypes existing in the different generations.
Providing there is no gene flow between the populations analysed, we would
expect to see that all the sampling areas would show similar frequencies,
but slightly differing phenotypes.
you haven't really said how you would incisively tell apart different explanations of the geographic pattern
Our null hypothesis would be that we would observe no trend or constant
correlation between frequency of dead and alive snails at a certain
location.
Through the following experiment we aim to determine the extent and effect
of genetic drift and natural selection on the speciation of snail
populations in a particular habitat. We will do this by observing
historical frequencies of snail phenotypes (in the form of discarded
shells and fragments) in given areas, and comparing them with the
phenotypes of the current living population in the same areas. The results
will determine which phenotypes are being more frequently selected for.
what is the logic here, if the dead are different from the live, that implies the allele frequency has changed, but that could be due to drift could it not?
Further to this we will compare the results between 3 or 4 populations to
discern whether the resulting phenotypes are based on natural selection or
genetic drift.
how will you tell them apart?
Here we hypothesize that we will observe a relatively constant correlation
between the phenotypic frequency of dead and living snails in a particular
location.
We can predict that the observations will show that natural selection is
working towards fixing a particular phenotype if those in historical
frequencies are the same as in current frequencies. what if the environment has changed. Eg you could see that bushes had recently been cut down to make more open areas However we can also
you haven't really said how you would incisively tell apart different explanations of the geographic pattern
Our null hypothesis would be that we would observe no trend or constant
correlation between frequency of dead and alive snails at a certain
location.
Contributing Members:
Jade Lam
Elisa Brann
Dominique Mckenzie-Spooner
Sioban Banful